Semiconductor device

ABSTRACT

A semiconductor memory array includes a first nonvolatile memory cell having a first charge storage layer and a first gate electrode and a second nonvolatile memory cell, adjacent to the first memory cell in a first direction, having a second charge storage layer and a second gate electrode. The first and second electrodes extend in a second direction perpendicular to the first direction, the first electrode has a first contact section extending toward the second electrode in the first direction, and the second electrode has a second contact section extending toward the first electrode in the first direction. The first and second contact positions are shifted in the second direction, respectively, and the first electrode and the first contact section are electrically separated from the second electrode and the second contact section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/970,703, filed Aug. 20, 2013, which, in turn, is a continuation ofU.S. application Ser. No. 13/653,544, filed Oct. 17, 2012 (nowabandoned), which, in turn, is a continuation of U.S. application Ser.No. 12/580,289, filed Oct. 16, 2009 (now U.S. Pat. No. 8,319,265),which, in turn, is a continuation of U.S. application Ser. No.12/354,867, filed Jan. 16, 2009 (now U.S. Pat. No. 7,636,253), which, inturn, is a continuation of U.S. application Ser. No. 11/797,164, filedMay 1, 2007 (now U.S. Pat. No. 7,502,257), which, in turn is aContinuation of U.S. application Ser. No. 11/198,191, filed Aug. 8, 2005(now U.S. Pat. No. 7,245,531), and which said application claimspriority from Japanese patent application No. 2004-231869 filed on Aug.9, 2004, the entire contents of which are hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, andparticularly to a technique effective if applied to a semiconductordevice including a nonvolatile semiconductor memory device.

As one of electrically programmable/erasable nonvolatile semiconductormemory devices, an EEPROM (Electrically Erasable and Programmable ReadOnly Memory) has been widely used. Each of these memories typified by aflash memory widely used at present has a conductive floating gateelectrode and a trap insulating film surrounded by an oxide film, whichare placed below a gate electrode of a MISFET, sets a charge storedstate at the floating gate or trap insulating film as memoryinformation, and reads it as the threshold voltage of the transistor.The trap insulating film corresponds to an insulating film capable ofstoring an electrical charge.

As one example, may be mentioned a silicon nitride film or the like. Thethreshold voltage of the MISFET is shifted by injection/discharge of theelectrical charge into and from such a charge storage region and thetrap insulating film is operated as a memory element. As the flashmemory, may be mentioned a split gate type cell using a MONOS(Metal-Oxide-Nitride-Oxide-Semiconductor) film. Such a memory has theadvantages that the use of the silicon nitride film as the chargestorage region brings about excellent reliability of data retentionbecause the electrical charge is stored on a discrete basis, as comparedwith a conductive floating gate film, and the oxide films provided aboveand below the silicon nitride film can be thinned because thereliability of the data retention is excellent, whereby reductions inthe voltages for write/erase operations are made possible.

A technique related to the layout of contacts relative to gateelectrodes of a nonvolatile semiconductor memory device has beendescribed in Japanese Unexamined Patent Publication No. 2003-100915(corresponding to USP 2003/0057505A1) (refer to a patent document 1).

A technique for applying different voltages to word lines of memorycells opposed with a bit line interposed therebetween upon a writeoperation has been described in Japanese Unexamined Patent PublicationNo. Hei 6 (1994)-333397 (refer to a patent document 2).

SUMMARY OF THE INVENTION

According to discussions made by the present inventors, the followinghave been found out.

In two memory cells adjacent to each other with a source regioninterposed therebetween such as shown in FIG. 8, the potential of eachsource region is always held at the same potential because the sourceregions are common. When the potentials of memory gate electrodes aretaken out from a common pad in the two memory cells adjacent to eachother with the source region interposed therebetween, the same potentialis always applied to the memory gate electrodes of the two memory cells.

When a predetermined write voltage is applied to respective portions ofa selected memory cell on which writing is effected, upon a writeoperation, source regions are common and held at the same potential inthe selected memory cell and a non-selected memory cell adjacent to theselected memory cell through the source region interposed therebetween.Further, their memory gate electrodes are also brought to the samepotential as described above. Therefore, when the write voltage isapplied to the selected memory cell, the same voltage as the selectedmemory cell is applied to the source region of the non-selected memorycell adjacent to the selected memory cell through the source regioninterposed therebetween, and its memory gate electrode.

Therefore, the potential of a select gate electrode of the non-selectedmemory cell adjacent to the writing selected memory cell through thesource region interposed therebetween cuts off a channel current andprevents disturb of the non-selected memory cell. In fact, however, ahigh voltage similar to the selected memory cell is applied to thesource region and memory gate electrode of the non-selected memory cellas described above. Therefore, a junction leak current occurs betweenthe source and substrate and hot electrons generated with is occurrenceare captured into a trap insulating film of the non-selected memorycell, thus causing a possibility that the threshold voltage of a memorytransistor of the non-selected memory cell will rise. Thus, the writedisturb applied to the non-selected memory cell adjacent to the writingselected memory cell through the source region interposed therebetweenbecomes a problem, thus causing a possibility that the performance ofthe semiconductor device will be degraded.

Unless the plane layout of the semiconductor device is designed inconsideration of a margin for alignment and a margin for a sizevariation in a photolithography process, etc., there is a possibilitythat the production yields of the semiconductor device will be degradedand the semiconductor device will be scaled up.

An object of the present invention is to provide a technique capable ofenhancing the performance of a semiconductor device.

Another object of the present invention is to provide a techniquecapable of improving production yields of a semiconductor device.

The above, other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

Summaries of representative ones of the inventions disclosed in thepresent application will be explained in brief as follows:

The present invention provides a semiconductor device. In thesemiconductor device, a plurality of memory cells are disposed in arrayform and include a plurality of select gate lines that connect selectgate electrodes of the memory cells arranged in a first direction, and aplurality of memory gate lines that connect memory gate electrodes ofthe memory cells arranged in the first direction, respectively. Thememory gate lines connected to their corresponding memory gateelectrodes of the memory cells adjacent to each other in a seconddirection orthogonal to the first direction through a source regioninterposed therebetween are not electrically connected to each other,and voltages can be applied thereto independently.

Also the present invention provides a semiconductor device. In thesemiconductor device, a plurality of memory cells are disposed in arrayform and include a plurality of select gate lines that connect selectgate electrodes of the memory cells arranged in a first direction, and aplurality of memory gate lines that connect memory gate electrodes ofthe memory cells arranged in the first direction. Each of the selectgate lines has a first portion extending in the first direction, and asecond portion of which one end is connected to the first portion andextends in a second direction intersecting the first direction. Each ofthe memory gate lines has a third portion adjacent to the first andsecond portions of the select gate line through an insulating filminterposed therebetween, and a fourth portion which is adjacent to thesecond portion of the select gate line through the insulating filminterposed therebetween and extends in a third direction that intersectswith the second direction. A conductor section embedded in a contacthole defined in an interlayer insulating film provided over the fourthportion of each memory gate line, and the fourth portion of the memorygate line are electrically connected.

Advantageous effects obtained by a representative one of the inventionsdisclosed in the present application will be described in brief asfollows:

The performance of a semiconductor device can be enhanced.

Production yields of the semiconductor device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary plan view of a semiconductor device according toa first embodiment of the present invention;

FIG. 2 is a fragmentary sectional view of the semiconductor deviceaccording to the first embodiment of the present invention;

FIG. 3 is a fragmentary sectional view of the semiconductor deviceaccording to the first embodiment of the present invention;

FIG. 4 is a fragmentary sectional view showing a typical sectionalstructure of a memory cell;

FIG. 5 is a table showing one example illustrative of a condition forapplication of voltages to respective portions of a selected memory cellat “write”, “erase” and “read”;

FIG. 6 is a fragmentary circuit diagram (equivalent circuit diagram) ofthe semiconductor device according to the first embodiment of thepresent invention;

FIG. 7 is a fragmentary plan view of the semiconductor device accordingto the first embodiment of the present invention;

FIG. 8 is a fragmentary plan view of a semiconductor device showing afirst comparative example;

FIG. 9 is a fragmentary sectional view of the semiconductor deviceillustrating the first comparative example;

FIG. 10 is an explanatory view showing problems at a write operation inthe semiconductor device of the first comparative example;

FIG. 11 is a graph illustrating write disturb of a non-selected memorycell at the operation of writing into the selected memory cell;

FIG. 12 is a fragmentary plan view of a semiconductor device showing asecond comparative example;

FIG. 13 is a fragmentary sectional view of the semiconductor deviceshowing the second comparative example;

FIG. 14 is a fragmentary sectional view in the process of manufacturingthe semiconductor device according to the first embodiment of thepresent invention;

FIG. 15 is a fragmentary sectional view in the process of manufacturingthe semiconductor device according to the first embodiment of thepresent invention;

FIG. 16 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 14;

FIG. 17 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 15;

FIG. 18 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 16;

FIG. 19 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 17;

FIG. 20 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 18;

FIG. 21 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 19;

FIG. 22 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 20;

FIG. 23 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 21;

FIG. 24 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 22;

FIG. 25 is a fragmentary sectional view in the process of manufacturingthe semiconductor device, following FIG. 23; and

FIG. 26 is a fragmentary plan view of a semiconductor device accordingto a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Whenever circumstances require it for convenience in the followingembodiments, they will be described with being divided into a pluralityof sections. However, unless otherwise specified in particular, they arenot irrelevant to one another. One thereof has to do with modifications,details and supplementary explanations of some or all of the other. Whenreference is made to the number of elements or the like (including thenumber of pieces, numerical values, quantity, range, etc.) in thefollowing embodiments, the number thereof is not limited to a specificnumber and may be greater than or less than or equal to the specificnumber unless otherwise specified in particular and definitely limitedto the specific number in principle. It is also needless to say thatcomponents (including element or factor steps, etc.) employed in thefollowing embodiments are not always essential unless otherwisespecified in particular and considered to be definitely essential inprinciple. Similarly, when reference is made to the shapes, positionalrelations and the like of the components or the like in the followingembodiments, they will include ones substantially analogous or similarto their shapes or the like unless otherwise specified in particular andconsidered not to be definitely so in principle, etc. This is similarlyapplied even to the above-described numerical values and range.

Preferred embodiments of the present invention will hereinafter beexplained with reference to the accompanying drawings. Incidentally,members each having the same function in all the drawings for describingthe embodiments are respectively given the same reference numerals andtheir repetitive explanations will be omitted. Unless necessary inparticular, the description of the same or similar parts will not berepeated in principle.

In the drawings used in the embodiments, some hatching might be omittedto make it easy to view the drawings even in the case of sectionalviews. Further, some hatching might be provided to make it easy to readthe drawings even in the case of plan views.

First Preferred Embodiment

A structure of a semiconductor device according to the presentembodiment will be explained with reference to the drawings. FIG. 1 is afragmentary plan view of the semiconductor device (nonvolatilesemiconductor memory device) of the present embodiment, and FIGS. 2 and3 are respectively fragmentary sectional views of the semiconductordevice according to the present embodiment, respectively. A sectiontaken along line A-A of FIG. 1 corresponds to FIG. 2, and a sectiontaken along line B-B of FIG. 1 corresponds to FIG. 3. For simplicity ofunderstanding, plane layouts of polycrystalline silicon films 6 each ofwhich forms a select gate electrode 8 and a select gate line 9,polycrystalline silicon films 12 each of which forms a memory gateelectrode 13 and a memory gate line 14, drain regions 19, source regions20 and contact holes 23, etc. are illustrated in FIG. 1. Illustrationsof other components are omitted. Sidewall spacers 18 are not illustratedin the plan view of FIG. 1. Low-concentration n-type semiconductorregions 16 and low-concentration n-type semiconductor regions 17 areillustrated so as to be included in the drain region 19 and the sourceregion 20 respectively.

The semiconductor device according to the present embodiment shown inFIGS. 1 through 3 is of a semiconductor device which includesnonvolatile semiconductor memory devices (nonvolatile memory and a flashmemory).

MISFETs (Metal Insulator Semiconductor Field Effect Transistors; MIStransistor and MIS type field effect transistor) each used as a memorycell of a nonvolatile memory are formed in memory cell regions (memorycell forming region and memory cell array forming region) of asemiconductor substrate (semiconductor wafer) 1 constituted of p-typemonocrystalline silicon or the like having specific resistivity rangingfrom approximately 1 to 10 Ωcm, for example.

Element isolation regions 2 for isolating elemental devices are formedin the semiconductor substrate 1. A p-type well 3 is formed in each ofactive regions separated by the element isolation regions 2. A memorycell 30 of a nonvolatile memory comprising a memory transistor and aselection transistor is formed in its corresponding p-type well 3 ofeach memory cell region 1A. A plurality of the memory cells 30 areformed in the individual memory cell regions 1A in array form. Therespective memory cell regions 1A are electrically isolated from otherregions by the element isolation regions 2.

Each memory cell 30 of the flash memory (nonvolatile semiconductormemory device) formed in the memory cell region 1A is of a split gatetype cell using a MONOS film. As shown in FIG. 2, each of the memorycells 30 includes an insulating film 11 formed as a gate insulating filmof a memory transistor, a memory gate electrode 13 (word line 13)constituted of a conductor like n-type polycrystalline silicon, a selectgate electrode (control gate electrode) 8 constituted of a conductorlike n-type polycrystalline silicon, a gate insulating film 5 locatedbelow the select gate electrode 8, a low-concentration n-typesemiconductor region (low-concentration n-type impurity region) 16 and adrain region (drain diffusion layer and high-concentration n-typesemiconductor region) 19 of a drain section, and a low-concentrationn-type semiconductor region (low-concentration n-type impurity region)17 and a source region (source diffusion layer and high-concentrationn-type semiconductor region) 20 of a source section. The memory gateelectrode 13 of each individual memory cell 30 constitutes a word lineof each memory cell. The select gate electrode 8 and memory gateelectrode 13 of each memory cell 30 are formed over the semiconductorsubstrate 1 located above between the drain region 19 and the sourceregion 20. The select gate electrode 8 is located on the drain region 19side. The memory gate electrode 13 is placed on the source region 20side and adjacent to the select gate electrode 8 with the insulatingfilm 11 interposed therebetween. The gate insulating film 5 isinterposed between the select gate electrode 8 and the semiconductorsubstrate 1. The insulating film 11 that serves as a gate insulatingfilm having a charge storage section is interposed between the memorygate electrode 13 and the semiconductor substrate 1. The memory gateelectrode 13 is formed over each sidewall of the select gate electrode 8in sidewall form with the insulating film 11 interposed therebetween.

Now, a MISFET constituted of the memory gate electrode 13 is called a“memory transistor”, and a MISFET constituted of the select gateelectrode (control gate electrode) 8 is called a “selection transistor(control transistor)”.

The memory cells 30 of the flash memory (nonvolatile semiconductormemory device) are arranged plural in array form over a main surface ofthe semiconductor substrate 1. The select gate electrodes 8 of thememory cells 30 arranged in an X direction (direction, i.e., firstdirection parallel to the main surface of the semiconductor substrate 1)of FIG. 1, of the plurality of memory cells 30 disposed in array form(matrix form) in the X and Y directions of FIG. 1 are electricallyconnected by their corresponding select gate lines 9 each formed of aconductor layer (i.e., polycrystalline silicon film 6) identical to theselect gate electrodes 8 in layer. The memory gate electrodes 13 of thememory cells 30 arranged in the X direction of FIG. 1 are electricallyconnected by their corresponding memory gate lines 14 each formed of aconductor layer (i.e., polycrystalline silicon film 12) identical to thememory gate electrodes 13 in layer. Each of the memory gate electrodes13 is adjacent to its corresponding select gate line 9 with theinsulating film 11 interposed therebetween. Each of the memory gatelines 14 is adjacent to its corresponding select gate line 9 with theinsulating film 11 interposed therebetween. Incidentally, the Ydirection of FIG. 1 corresponds to the direction that intersects the Xdirection, and may preferably be a direction normal to the X direction.

The gate insulating film 5 is constituted of an insulating film such asa silicon oxide film. The insulating film 11 is of an insulating film(trap-like insulating film) having a charge storage section thereinside.For instance, the insulating film comprises a laminated or stacked film(ONO (Oxide-Nitride-Oxide) film) of a silicon nitride film (i.e., chargestorage section) for storing an electrical charge, and silicon oxidefilms located thereabove and therebelow. Each of the insulating films 11is formed below the memory gate electrode 13, below the memory gate line14, between the adjacent select gate electrode 8 and memory gateelectrode 13 and between the adjacent select gate line 9 and memory gateline 14. The insulating film 11 placed below the memory gate electrode13 is used as a gate insulating film (gate insulating film having chargestorage section thereinside) of each memory transistor.

Each of the low-concentration n-type semiconductor region 16,low-concentration n-type semiconductor region 17, drain region 19 andsource region 20 comprises a semiconductor region (silicon region) inwhich an n-type impurity (e.g., Phosphorous (P) or Arsenic (As) or thelike) has been introduced, and is formed in the p-type well 3 providedin the semiconductor substrate 1. The drain region 19 is higher than thelow-concentration n-type semiconductor region 16 of the drain section inimpurity concentration, and the source region 20 is higher thanlow-concentration n-type semiconductor region 17 of the source sectionin impurity concentration. Of the plurality of memory cells 30, the(adjoining) memory cells 30 adjacent to one another in the Y directionof FIG. 1 through the drain regions 19 respectively share the drainregions 19. Also the (adjoining) memory cells 30 adjacent to one anotherin the Y direction of FIG. 1 through the source regions 20 respectivelyshare the source regions 20.

Sidewall spacers 18 each formed of an insulating film such as siliconoxide are formed over their corresponding sidewalls of the select gateelectrodes and their corresponding sidewalls of the memory gateelectrodes 13. That is, each of the sidewall spacers 18 is formed overits corresponding sidewall of the memory gate electrode 13 on the sideopposite to the side adjacent to the select gate electrode 8 with theinsulating film 11 interposed therebetween and over its correspondingsidewall of the select gate electrode 8 on the side opposite to the sideadjacent to the memory gate electrode 13 with the insulating film 11interposed therebetween.

Each of the low-concentration n-type semiconductor regions 16 of thedrain section is formed on a self-alignment basis with respect to itscorresponding select gate electrode 8. Each of the drain regions 19 isformed on a self-alignment basis with respect to its correspondingsidewall spacer 18 placed over each sidewall of the select gateelectrode 8. Therefore, the low-concentration n-type semiconductorregion 16 is formed below the sidewall spacers 18 placed over the selectgate electrode 8, and the drain region 19 is formed outside thelow-concentration n-type semiconductor region 16. Thus, thelow-concentration n-type semiconductor region 16 is formed so as to beadjacent to a channel region of each selection transistor. The drainregion 19 is held close to the low-concentration n-type semiconductorregion 16 and formed so as to be spaced away from the channel region ofthe selection transistor by the low-concentration n-type semiconductorregion 16. The low-concentration n-type semiconductor region 17 of thesource section is formed on a self-alignment basis with respect to itscorresponding memory gate electrode 13, and the source region 20 isformed on a self-alignment basis with respect to the sidewall spacers 18placed over the sidewalls of the memory gate electrodes 13. Therefore,the low-concentration n-type semiconductor region 17 is formed below itscorresponding sidewall spacer 18 placed over the sidewall of the memorygate electrode 13, and the source region 20 is formed outside thelow-concentration n-type semiconductor region 17. Thus, thelow-concentration n-type semiconductor region 17 is formed so as toadjoin the channel region of the memory transistor. The source region 20is held close to the low-concentration n-type semiconductor region 17and formed so as to be spaced away from the channel region of the memorytransistor by the low-concentration n-type semiconductor region 17.

Each of the select gate electrodes 8 is formed by patterning apolycrystalline silicon film (polycrystalline silicon film implantedwith an n-type impurity or doped therewith) 6 formed over thesemiconductor substrate 1. The patterned polycrystalline silicon films 6that form the select gate electrodes 8 extend in the X direction of FIG.1 and connect the select gate electrodes 8 of the individual memorycells 30 to one another. Thus, the patterned polycrystalline siliconfilms 6 form the select gate electrodes 8 of the respective memory cells30 and the select gate lines 9 that connect between the select gateelectrodes 8 of the memory cells 30 arranged in the X direction ofFIG. 1. That is, the select gate electrodes 8 and the select gate lines9 are formed by the conductor films (conductor layers) identical inlayer formed in the same process.

The memory gate electrodes 13 are formed by anisotropically etching thepolycrystalline silicon films (polycrystalline silicon films eachimplanted with an n-type impurity or doped therewith) 12 formed over thesemiconductor substrate 1 so as to cover the select gate electrodes 8and allowing the polycrystalline silicon films 12 to remain over thesidewalls of the select gate electrodes 8 with the insulating films 11each interposed therebetween. The polycrystalline silicon films 12 thatform the memory gate electrodes 13 are formed over one sidewalls of thepatterned polycrystalline silicon films 6 that constitute the selectgate electrodes 8 and the select gate lines 9 and extend in the Xdirection (transverse direction) of FIG. 1, and connect the memory gateelectrodes 13 of the respective memory cells 30 to one another. Thus,the polycrystalline silicon films 12 provided over the sidewalls of thepatterned polycrystalline silicon films 6 that constitute the selectgate electrodes 8 and the select gate lines 9 form the memory gateelectrodes 13 of the respective memory cells 30 and the memory gatelines 14 that connect between the memory gate electrodes 13 of thememory cells 30 arranged in the X direction of FIG. 1. The memory gatelines 14 are formed in a word shunt region 1C that connect therespective memory cell regions 1A and disposed such that a commonpotential is applied to the memory cells 30 of the respective memorycell regions 1A, and connect the memory gate electrodes 13 of therespective memory cells 30. That is, the memory gate electrodes 13 andthe memory gate lines 14 are formed by the conductor films (conductorlayers) identical in layer formed in the same process. Thepolycrystalline silicon film 12 formed over one sidewall of each selectgate electrode 8 with the insulating film 11 interposed therebetweenresults in the memory gate electrode 13, whereas the polycrystallinesilicon film 12 formed over one sidewall of each select gate line 9 withthe insulating film 11 interposed therebetween results in the memorygate line 14.

The select gate electrode 8 and the memory gate electrode 13 of each ofthe selection transistor and the memory transistor that respectivelyconstitute the memory cells 30 are adjacent to each other with theinsulating film 11 interposed therebetween. Further, the select gateline 9 and the memory gate line 14 are adjacent to each other with theinsulating film 11 interposed therebetween. A channel region of thememory transistor is formed below its corresponding insulating film 11placed below the memory gate electrode 13, and a channel region of theselection transistor is formed below its corresponding gate insulatingfilm 5 placed below the select gate electrode 8.

A p-type semiconductor region 4 for adjustment of the threshold voltageof the selection transistor is formed as needed in a channel formingregion of the selection transistor placed below the gate insulating film5 provided below each select gate electrode 8, whereas a p-typesemiconductor region (or n-type semiconductor region) 10 for adjustmentof the threshold voltage of the memory transistor is formed as needed ina channel forming region of the memory transistor placed below theinsulating film 11 provided below each memory gate electrode 13.

A metal silicide film 21 (e.g., cobalt silicide film) is formed overupper surfaces (surfaces) of the select gate electrodes 8, select gatelines 9, memory gate electrodes 13, memory gate lines 14, drain regions19 and source regions 20 by a salicide process or the like. The metalsilicide film 21 can bring a diffusion resistance and a contactresistance into low-resistance form.

An insulating film (interlayer insulating film) 22 is formed as aninterlayer insulating film so as to cover the select gate electrodes 8and the memory gate electrodes 13. The insulating film 22 comprises, forexample, a laminated film or the like of relatively thin silicon nitride22 a and relatively thick silicon oxide 22 b provided thereon. Thesilicon nitride 22 a can function as an etching stopper film at theformation of each contact hole 23. The contact holes (openings) 23 aredefined in the insulating film 22, and plugs (conductor sections) 24each formed of a conductive film constituted principally of a tungsten(W) film are formed in their corresponding contact holes 23. A wiring(first wiring layer) 25 is formed over the insulating film 22 with theplugs 24 embedded therein. The wiring 25 is of an aluminum wiringconstituted of, for example, a laminated or stacked film of a barrierconductor film 25 a, an aluminum film 25 b and a barrier conductor film25 c. The barrier conductor films 25 a and 25 c are respectively made upof, for example, a titanium film, a titanium nitride film or theirlaminated film. The wiring 25 is not limited to the aluminum wiring andcan be altered in various ways. The wiring 25 can also be constitutedas, for example, a tungsten wiring or copper wiring (buried copperwiring formed by the damascene method, for example).

Of the contact holes 23 and the plugs 24 that bury them, contact holes23 a for connecting to the drain regions 19 and plugs 24 a that burythem are formed over the drain regions 19 of the respective memory cells30 of each memory cell region 1A. Contact holes 23 b for connecting tothe source regions 20 and plugs 24 b that bury them are formed over thesource regions 20 of a source dummy region 1B at an end (outerperipheral portion) of each memory cell region 1A. Contact holes 23 cfor connecting to the select gate lines 9 and plugs 24 c that bury themare formed over the select gate lines 9 of the word shunt region 1Cbetween the memory cell regions 1A. Contact holes 23 d for connecting tothe memory gate lines 14 and plugs 24 d that bury them are formed overthe memory gate lines 14 of the word shunt region 1C between the memorycell regions 1A. Incidentally, an element isolation region 2 is formedin the word shunt region 1C over its entirety, and the select gate lines9 and the memory gate lines 14 are formed over the element isolationregion 2 of the word shunt region 1C. Since the contact holes 23 b forconnecting to the source regions 20 and the plugs 24 b that bury themare disposed in the source dummy region 1B at the end (outer peripheralportion) of each memory cell region 1A, the source dummy region 1B istaken as a memory cell dummy region and results in a measure against acrystal defect.

The select gate lines 9 and the memory gate lines 14 will next beexplained in more detail.

Each of the select gate lines 9 has a first portion 9 a which extends inthe X direction of FIG. 1 and connects the select gate electrodes 8 ofthe memory cells 30 arranged in the X direction to one another, and asecond portion 9 b whose one end is connected to the first portion 9 aand extends in the Y direction (the direction, i.e., second directionparallel to the main surface of the semiconductor substrate 1 andorthogonal to the X direction). That is, the second portion 9 b of theselect gate line 9 extends in the direction that intersects with thedirection in which the first portion 9 a extends, more preferably in thedirection orthogonal (vertical) to the direction in which the firstportion 9 a extends.

The distance from the end of the second portion 9 b extended in the Ydirection to the select gate line 9 (first portion 9 a) opposite theretothrough the source region and the memory gate line 14 is shorter thanthe length of the second portion 9 b as viewed in the Y direction. Thatis, the length of the second portion 9 b as viewed in the Y direction iscaused to extend where practicable in terms of design dimensions. It isthus possible to easily ensure space as viewed in the Y direction for acontact section 14 a of each memory gate line, which is formed so as toextend in the X direction from the second portion 9 b and to make iteasy to prevent each contact hole 23 d from misalignment.

Further, the length as viewed in the Y direction, of the second portion9 b of the select gate line is formed so as to be longer than the lengththereof as viewed in the X direction. Thus, since the length necessaryto extend the contact section 14 a of the memory gate line in the Xdirection can be lengthened, it is possible to make it easy to preventthe contact hole 23 d from misalignment.

The first portion 9 a of each select gate line 9 is relatively made widein width (width in the Y direction) at a portion below each contact hole23 c. The contact hole 23 c is formed over its corresponding wideportion (third portion) 9 c of the first portion 9 a of the select gateline 9. Each of the plugs 24 c is connected to its corresponding wideportion 9 c of the first portion 9 a of the select gate line 9 at thebottom of the contact hole 23 c. Forming the contact holes 23 c over thewide portions 9 c relatively broad in width and connecting the plugs 24c embedded in the contact holes 23 c to the wide portions 9 crespectively make it possible to prevent the contact holes 23 c frombeing misaligned, assuredly expose the select gate lines 9 at thebottoms of the contact holes 23 c and reliably connect (electricallyconnect) the plugs 24 c to the select gate lines 9 respectively. It isalso possible to prevent the memory gate lines 14 from being exposed atthe bottoms of the contact holes 23 c and prevent the select gate lines9 and the memory gate lines 14 from being short-circuited. Incidentally,the first portion 9 a, second portion 9 b and wide portion 9 c of eachselect gate line 9 are constituted of the patterned polycrystallinesilicon films 6 as described above.

The memory gate line 14 is formed over one sidewall of the select gateline 9 with the insulating film 11 interposed therebetween. Thus, thememory gate line 14 is formed over its corresponding sidewalls of thefirst portion 9 a, second portion 9 b and wide portion 9 c of eachselect gate line 9 with the insulating film 11 interposed therebetween.While the memory gate line 14 is formed on one sidewall of the selectgate line 9 in sidewall form with the insulating film 11 interposedtherebetween, it is further adjacent to the second portion 9 b of theselect gate line 9 through the insulating film 11 and has thecorresponding contact section 14 a that extends in the X direction ofFIG. 1. The contact section 14 a of the memory gate line 14 is also madeup of the polycrystalline silicon film 12 in a manner similar to thesidewalled portion of the memory gate line 14. Thus, the contact section14 a of the memory gate line 14 extends in the direction that intersectswith the direction (Y direction) in which the second portion 9 b of theselect gate line 9 extends, more preferably, extends in the direction(direction orthogonal to the direction (Y direction) in which the secondportion 9 a extends) parallel to the X direction of FIG. 1. Since theelement isolation region 2 is formed over the entire word shunt region1C as described above and the select gate lines 9 and memory gate lines14 are formed over the element isolation region 2, the contact sections14 a of the memory gate lines 14 extend in the X direction of FIG. 1from over the second portions 9 b of the select gate lines 9 to over theelement isolation region 2. The insulating film 11 is interposed betweenthe contact section 14 a of each memory gate line 14 and the secondportion 9 b of each select gate line 9.

As described above, the memory gate electrodes 13 and the memory gatelines 14 each comprising the polycrystalline silicon film 12 can beformed by anisotropically etching the polycrystalline silicon films 12formed over the semiconductor substrate 1 so as to cover the patternedpolycrystalline silicon films 6 constituting the select gate electrodes8 and the select gate lines 9 and allowing the polycrystalline siliconfilms 12 to remain over one sidewalls of the patterned polycrystallinesilicon films 6 with the insulating films 11 each interposedtherebetween. In the anisotropic etching process of the polycrystallinesilicon films 12, an etching mask layer (photoresist layer not shown) isformed over each contact section 14 a and the polycrystalline siliconfilm 12 below the etching mask layer is caused to remain, whereby thecontact section 14 a of each select gate line 9 is formed. Thus, a planpattern shape of the etching mask layer (photoresist layer) used at thistime corresponds to a plan pattern shape of the contact section 14 a.Accordingly, the memory gate electrodes 13, the memory gate lines 14 andthe contact sections 14 a of the memory gate lines 14 are formed of thesame conductor layers (polycrystalline silicon films 12 in the presentembodiment).

The contact holes 23 d are formed over the contact sections 14 a of thememory gate lines 14. The plugs 24 d are electrically connected to theircorresponding contact sections 14 a of the memory gate lines 14 at thebottoms of the contact holes 23 d. The plan pattern shape of eachcontact section 14 a is formed in such a predetermined size as not tocause misalignment in consideration of a displacement of the contacthole 23 d at its opening. It is thus possible to prevent misalignment ofthe contact holes 23 d, reliably expose the contact sections 14 a of thememory gate lines 14 at the bottoms of the contact holes 24 d andassuredly connect (electrically connect) the plugs 24 d to the memorygate lines 14. The contact sections 14 a of the memory gate lines 14extend from over the second portions 9 b of the select gate lines 9 toover the corresponding element isolation region 2 respectively, and thecontact holes 23 d are respectively formed over the contact sections 14a located above the corresponding element isolation region 2. Therefore,since the contact sections 14 a of the memory gate lines 14 and theelement isolation region 2 are exposed at the bottoms of the contactholes 23 d even though misalignment occurs in the contact holes 23 d,the plugs 24 d embedded into the misaligned contact holes 23 d can beprevented from being shorted with other conductive members. Since theelement isolation region 2 is exposed at the bottom of each contact hole23 d even if overetching occurs in the forming process of the contacthole 23 d, each of the plugs 24 d embedded in the contact holes 23 d canbe prevented from being shorted with other conductive member. Further,electrical connections between the plugs 24 d and the contact sections14 d of the memory gate lines 14 can be ensured by contact between thelower side faces of the plugs 24 d and the contact sections 14 a of thememory gate lines 14.

In the present embodiment, the respective memory gate lines 14 areprovided with the independent contact sections 14 a respectively. The(two) memory gate lines 14 respectively connected to the memory gateelectrodes 13 of the memory cells 30, which adjoin each other (areadjacent and opposite to each other) through the source region 20 (beinginterposed therebetween) as viewed in the Y direction of FIG. 1, are notelectrically connected to each other.

Incidentally, the memory cell 30 a and the memory cell 30 b has therelationship that they adjoin each other in the Y direction with thesource region 20 interposed therebetween (they are adjacent and oppositeto each other) in FIG. 2 by way of example. In the present embodiment,the (two) memory gate lines 14 respectively connected to the memory gateelectrodes 13 of the memory cells 30 (e.g., the memory cell 30 a andmemory cell 30 b in FIG. 2), which adjoin each other in the Y directionof FIG. 1 with the source region 20 interposed therebetween, will bereferred to as the (two) memory gate lines 14 adjacent to each other inthe Y direction of FIG. 1 with the source region 20 interposedtherebetween.

In the present embodiment, the (two) memory gate lines 14 adjacent toeach other in the Y direction of FIG. 1 with the source region 20interposed therebetween are displaced or shifted in the X direction ofFIG. 1 in terms of the positions for connections of the contact sections14 a and plugs 24 d in the word shunt region 1C. The memory gate lines14 are respectively electrically connected to different wirings 25 (25d) which are formed over the insulating film 22 and extend in the Ydirection. That is, the memory gate lines 14 are electrically connectedvia the plugs 24 d and wirings 25 (25 d) to other memory gate lines 14other than the memory gate lines 14 adjacent to one another in the Ydirection with the source region 20 interposed therebetween. In theexample shown in FIG. 1, the memory gate lines 14 are electricallyconnected on alternate lines through the plugs 24 d and wirings 25(wirings 25 d). Therefore, the (two) memory gate lines 14 respectivelyconnected to the memory gate electrodes 13 of the memory cells 30adjacent to each other in the Y direction of FIG. 1 with the sourceregion 20 interposed therebetween, i.e., the (two) memory gate lines 14adjacent to each other in the Y direction with the source region 20interposed therebetween are configured in such a manner that desiredvoltages (different voltages) can independently be applied theretothrough the plugs 24 d and contact sections 14 a. Therefore, in thepresent embodiment, independent different voltages (potentials) canrespectively be applied to the memory gate electrodes 13 of the memorycells 30 (e.g., the memory cell 30 a and the memory cell 30 b) adjacentto each other in the Y direction with the source region 20 interposedtherebetween.

Since a process margin is easily ensured in the present embodiment aswill be described later, it is possible to form the metal silicide film21 over the upper surfaces of the select gate lines 9 and the memorygate lines 14, prevent a break in the metal silicide film 21 and bringthe select gate lines 9 and the memory gate lines 14 into low-resistanceform. It is therefore possible to bring the number of the plugs 24connected to the respective select gate lines 9 and the memory gatelines 14 into one. Thus, a reduction in plane layout area of thesemiconductor device and the like can be carried out.

FIG. 4 is a fragmentary sectional view showing a typical sectionalstructure of a memory cell 30 employed in the semiconductor deviceaccording to the present embodiment. FIG. 5 is a table showing oneexample illustrative of a condition for application of voltages torespective portions of a selected memory cell at “write”, “erase” and“read”. At the “write”, “erase” and “read”, a voltage Vd applied to adrain region 19 of such a memory cell (selected memory cell) as shown inFIG. 4, a voltage Vcg applied to a select gate electrode 8 (select gateline 9), a voltage Vmg applied to a memory gate electrode 13 (memorygate line 14), a voltage Vs applied to a source region 20, and a basevoltage Vb applied to a p-type well 3 are described in Table shown inFIG. 5. Incidentally, ones shown in Table of FIG. 5 are shown as oneexample illustrative of the voltage application condition. The voltageapplication condition is not limited to it and can be altered in variousways as needed. In the present embodiment, the implantation of electronsinto a silicon nitride film corresponding to a charge storage section inan insulating film of a memory transistor will be defined as “write” andthe injection of holes (positive holes) therein will be defined as“erase”, respectively. As shown in FIG. 4, the insulating film 11comprises a laminated film (ONO film) of a silicon oxide film 11 a, asilicon nitride film 11 b and a silicon oxide film 11 c. The siliconnitride film 11 b serves as the charge storage section for storing anelectrical charge therein.

As a write method, hot electron write called “so-called source sideinjection system” can be used. For example, such voltages as shown inthe column of “write” in FIG. 5 are applied to respective portions of aselected memory cell on which writing is effected, and electrons areimplanted into the silicon nitride film 11 b of the insulating film 11of the selected memory cell. Hot electrons are generated in a lowerchannel region (between the source and drain) between the two gateelectrodes (memory gate electrode 13 and select gate electrode 8). Thehot electrons are locally injected into a region on the selectiontransistor side, of the silicon nitride film 11 b corresponding to thecharge storage section in the insulating film 11 below the memory gateelectrode 13. The injected hot electrons are captured into a trap in thesilicon nitride film 11 b of the insulating film 11. As a result, thethreshold voltage of the memory transistor rises.

An erase method can make use of a BTBT (Band-To-Band Tunneling) hot holeinjection erase system. That is, holes (positive holes) generated by theBTBT are injected into the charge storage section (the silicon nitridefilm 11 b of the insulating film 11) to thereby perform erasing. Forexample, such voltages as shown in the column of “erase” of FIG. 5 areapplied to respective portions of a selected memory cell on whicherasing is effected, and holes (positive holes) are generated by theBTBT to accelerate an electric field, thereby injecting the holes intothe silicon nitride film 11 b of the insulating film 11 of the selectedmemory cell, whereby the threshold voltage of the memory transistor isreduced.

Upon reading, for example, such voltages as shown in the column of“read” of FIG. 5 are applied to respective portions of a selected memorycell to be read. By setting the voltage Vmg applied to the memory gateelectrode 13 at the reading to a value between the threshold voltage ofthe memory transistor in a write state and the threshold voltage thereofin an erase state, the write state and the erase state can bediscriminated.

FIG. 6 is a fragmentary circuit diagram (equivalent circuit diagram) ofthe semiconductor device according to the present embodiment. As showneven in the circuit diagram of FIG. 6, a plurality of memory cells 30are formed in each memory cell region 1A and disposed in array form.Drain regions 19 of the respective memory cells 30 are connected totheir corresponding bit lines BL1 through BL6 (comprising wirings 25)that extend in a Y direction. Source regions (20) of the respectivememory cells 30 are connected to their corresponding source lines MSL1and MSL2 (comprising wirings 25) that extend in the Y direction, insource dummy regions 1B. Select gate electrodes (8) of the memory cells30 arranged in an X direction are electrically connected by theircorresponding select gate lines CGL1 through CGL4 (corresponding toselect gate lines 9). Memory gate electrodes (13) of the memory cells 30arranged in the X direction are electrically connected by theircorresponding memory gate lines MGL1 through MGL4 (corresponding tomemory gate lines 14). The memory gate lines MG11 through MGL4 areconnected to their corresponding memory gate wirings MMG1 and MMG2(comprising wirings 25) extending in the Y direction in a word shuntregion 1C. As shown even in the circuit diagram of FIG. 6, the memorygate lines, the memory gate line MGL2 and memory gate line MGL3 in theexample of FIG. 6 respectively connected to the memory gate electrodes(13) of the memory cells 30 adjacent to each other in the Y directionwith the source regions thereof interposed therebetween are notelectrically connected to each other. One memory gate line MGL2 isconnected to the memory gate wiring MMG1 in the word shunt region 1C,whereas the other memory gate line MGL3 is connected to the other memorygate wiring MMG2 in the word shunt region 1C. Therefore, predetermined(desired) voltages can independently be applied to the memory gate linesadjacent to each other in the Y direction with the source regions 20thereof interposed therebetween, i.e., the memory gate line MGL2 and thememory gate line MGL3 in the present example through the memory gatelines MMG1 and MMG2. Therefore, different voltages (potentials) can beapplied to the memory gate lines (memory gate lines MGL2 and MGL3 in thepresent example) adjacent to each other in the Y direction with thesource regions 20 interposed therebetween, through the memory gatewirings MMG1 through MMG2. Accordingly, the voltages can independentlybe applied to the memory gate electrodes of the memory cells 30 adjacentto each other through the source regions 20 thereof and hence differentvoltages can be applied thereto respectively.

FIG. 7 is a fragmentary plan view of the semiconductor device accordingto the present embodiment. The figure corresponds to one in whichwirings 25 d (i.e., wirings 25 d corresponding to the memory gatewirings MMG1 and MMG2 shown in FIG. 6) connected to the memory gatelines 14, of the wirings 25 are further added to and described inFIG. 1. In the word shunt region 10, the wirings 25 d are electricallyconnected to their corresponding contact sections 14 a of the memorygate lines 14 through the plugs 24 d that bury the contact holes 23 d.As shown in FIG. 7, the (two) memory gate lines 14 respectivelyconnected to the memory gate electrodes 13 of the memory cells 30adjacent to each other in the Y direction with the source region 20interposed therebetween, i.e., the (two) memory gate lines 14 adjacentto each other in the Y direction with the source region 20 interposedtherebetween are not electrically connected to each other. One memorygate line 14 is connected to its corresponding wiring 25 d in the wordshunt region 1C, whereas the other memory gate line 14 is connected toits corresponding other wiring 25 d in the word shunt region 1C.Therefore, predetermined (desired) voltages can independently be appliedto the (two) memory gate lines 14 adjacent to each other with the sourceregion 20 interposed therebetween, through the wirings 25 d. Differentvoltages (potentials) can be applied to the (two) memory gate lines 14adjacent to each other with the source region 20 interposedtherebetween, through the wirings 25 d.

FIG. 8 is a fragmentary plan view of a semiconductor device (nonvolatilesemiconductor memory device) showing a first comparative examplediscussed by the present inventors. FIG. 9 is a fragmentary sectionalview thereof. A sectional view taken along line C-C of FIG. 8corresponds to FIG. 9. Also FIG. 8 is a plan view corresponding to FIG.1 referred to above.

The semiconductor device showing the first comparative example shown inFIGS. 8 and 9 is different from the semiconductor device according tothe present embodiment in terms of pattern shapes of select gate lines 9and memory gate lines 14, positions of contact holes 23 e connected tothe memory gate lines 14 and plugs 24 e that bury them, and arelationship of connection between wirings 25 connected to the plugs 24e and the memory gate lines 14. Since a sectional structure of eachmemory cell of the semiconductor device according to the firstcomparative example is similar to that of FIG. 2 of the firstembodiment, its explanation will be omitted herein.

In the semiconductor device of the first comparative example shown inFIGS. 8 and 9, in a manner similar to the present embodiment, the selectgate lines 9 comprises patterned polycrystalline silicon films 6 andrespectively have first portions 9 a that connect select gate electrodes8 of memory cells 30 extending in an X direction (corresponding to the Xdirection of FIG. 1) of FIG. 8 and arranged in the X direction, and wideportions 9 c each relatively broad in width at the first portion 9 a.However, the select gate lines 9 are not provided with the secondportions 9 b unlike the present embodiment.

In the semiconductor device of the first comparative example shown inFIGS. 8 and 9, each of the memory gate lines 14 each constituted of apolycrystalline silicon film 12 is formed over one sidewall of each ofthe select gate lines 9 with an insulating film 11 interposedtherebetween. The memory gate lines 14 adjacent to one another through asource region 20 in a Y direction are electrically connected to oneanother by contact sections 14 b each made up of some of thepolycrystalline silicon films 12 that constitute the memory gate lines14. The contact sections 14 b extend in the Y direction (correspondingto the Y direction of FIG. 1) of FIG. 8 from over the select gate lines9 to over the other select gate lines 9, and electrically connect thememory gate lines 14 provided over the sidewalls of the select gatelines 9 and other memory gate lines 14 provided over the sidewalls ofthe other select gate lines 9, respectively.

The polycrystalline silicon films 12 formed over a semiconductorsubstrate 1 so as to cover patterned polycrystalline silicon films 6that constitute the select gate electrodes 8 and the select gate lines 9are anisotropically etched to allow the polycrystalline silicon films 12to remain on one sidewalls of the patterned polycrystalline siliconfilms 6 with the insulating films 11 interposed therebetween.Consequently, the corresponding memory gate electrodes 13 and memorygate lines 14 each formed of the polycrystalline silicon film 12 can beformed. On the other hand, however, an etching mask layer (photoresistlayer not shown) is formed over the contact sections 14 b and thepolycrystalline silicon films 12 placed below the etching mask layer arecaused to remain in the process of anisotropically etching thepolycrystalline silicon films 12, whereby the contact sections 14 b ofthe memory gate lines 14 are formed. Thus, the plan pattern shape of theetching mask layer (photoresist layer) used at this time corresponds tothat of each contact section 14 b.

The contact hole 23 e is formed over its corresponding contact section14 b of the memory gate line 14. The plug 24 e is connected to itscorresponding contact section 14 b of the memory gate line 14 at thebottom of the contact hole 23 e. The plug 24 e is connected to thewiring 25 and a plurality of the memory gate lines 14 are electricallyconnected through the plugs 24 e and wirings 25. Thus, in the firstcomparative example, the two memory gate lines 14 (memory gateelectrodes 13) adjacent to each other in the Y direction through thesource region 20 interposed therebetween are taken out (led out) by thecommon contact section 14 b and the plug 24 e connected thereto.

FIG. 10 is an explanatory view showing problems at a write operation inthe semiconductor device of the first comparative example.

In the semiconductor device of the first comparative example shown inFIGS. 8 and 9, such voltages as shown in the column of “write” of FIG. 5are applied to respective portions of the corresponding selected memorycell to be written of the memory cells 30 upon the write operation. Inthe selected memory cell, 1V is applied to the drain region 19 as Vd,1.5V (Vdd) is applied to the select gate electrode 8 (select gate line9) as Vcg, 12V is applied to the memory gate electrode 13 (memory gateline 14) as Vmg, and 6V is applied to the source region 20 as Vs. In theselected memory cell and a non-selected memory cell (memory cell onwhich no writing is performed) that adjoin (is adjacent to) the selectedmemory cell in the Y direction through the source region 20 interposedtherebetween, the source region 20 is common and the memory gate lines14 are electrically connected to each other at the contact section 14 b.Therefore, the potential Vs of the source region 20 becomes the samepotential because the source region 20 is common in the selected memorycell and the non-selected memory cell adjacent to the selected memorycell in the Y direction with the source region 20 interposedtherebetween. Since the memory gate lines 14 are connected to each otherat the contact section 14 b, the potentials Vmg of the memory gateelectrodes 13 (memory gate lines 14) become the same potential. Thus,when the write voltage is applied to the selected memory cell, the samevoltages (Vs=6V and Vmg=12V) as the selected memory cell are applied tothe source region 20 of the non-selected memory cell and the memory gateelectrode 13 (memory gate line 14).

Therefore, a channel current is cut off by the potential Vcg of theselect gate electrode 8 (select gate line 9) of the non-selected memorycell adjacent to the selected memory cell to be written in the Ydirection with the source region 20 interposed therebetween, thereby toprevent disturb of the non-selected memory cell. Since, however, a highvoltage similar to the selected memory cell is actually applied to thesource region 20 and memory gate electrode 13 in the non-selected memorycell adjacent to the selected memory cell to be written in the Ydirection through the source region 20 as shown in FIG. 10 and in theabove, a junction leak current occurs between the source and substrateand hot electrons generated with its occurrence are captured into thecorresponding insulating film 11 (silicon nitride film 11 b thereof) ofthe non-selected memory cell, thus causing the possibility that thethreshold voltage of a memory transistor for the non-selected memorycell will rise. Thus, the write disturb applied to the non-selectedmemory cell adjacent to the writing selected memory cell in the Ydirection through the source region 20 becomes a problem. This causesthe possibility that the performance of the semiconductor device will bedegraded.

In the present embodiment in contrast, the memory gate lines 14respectively connected to the memory gate electrodes 13 of the memorycells 30, which adjoin (are opposite and adjacent to one another) in theY direction with the source regions 20 interposed therebetween, i.e.,the memory gate lines 14 adjacent to one another in the Y direction withthe source regions 20 interposed therebetween are not electricallyconnected to one another as mentioned above. Further, the voltages(different voltages) can independently be applied thereto through thedifferent wirings 25 d and plugs 24 d. Thus, in the present embodiment,the two memory gate lines 14 (memory gate electrodes 13) adjacent toeach other in the Y direction with the source region 20 interposedtherebetween are respectively independently be taken out (led out) bythe contact sections 14 a of the respective memory gate lines 14 and theplugs 24 d connected thereto. Therefore, the selected memory cellintended for writing, of the memory cells 30 and the non-selected memorycell adjacent to the selected memory cell in the Y direction with thesource region 20 interposed therebetween make it possible toindependently apply (supply) predetermined (desired) voltages to thememory gate electrodes 13. Thus, different potentials can be applied(supplied) to the memory gate electrode 13 of the selected memory cellon which writing is performed, and the memory gate electrode 13 of thenon-selected memory cell adjacent to the selected memory cell in the Ydirection with the source region 20 interposed therebetween.

Therefore, in the present embodiment, even though such voltages as shownin the column of “write” of FIG. 5 are applied to the respectiveportions of the selected memory cell intended for writing upon a writeoperation, the value of the voltage applied to the memory gate electrode13 in the non-selected memory cell adjacent to the selected memory cellin the Y direction with the source region 20 interposed therebetween canbe made different from the value of the voltage applied to the memorygate electrode 13 of the selected memory cell. For example, the voltageVmg of the memory gate electrode 13 of the non-selected memory celladjacent to the writing selected memory cell in the Y direction with thesource region 20 interposed therebetween can be made lower than thevoltage Vmg (12V in the example of FIG. 5) of the memory gate electrode13 of the writing selected memory cell (the former voltage is set to,for example, 0V or 1.5V or the like as Vdd). That is, in the presentembodiment, the value of a voltage applied to a word line (memory gateelectrode 13) of a selected memory cell intended for writing, of atleast two memory cells (corresponding to the memory cells 30 a and 30 b,for example) connected to a common source line and disposed adjacent toeach other so as to be opposed to the source line is rendered differentfrom the value of a voltage applied to a word line (memory gate line 13)of the non-selected memory cell unintended for writing upon writeoperations of the memory cells. More preferably, the value of thevoltage applied to the word line (memory gate electrode 13) of theselected memory cell is made greater than the value of the voltageapplied to the word line (memory gate electrode 13) of the non-selectedmemory cell. It is thus possible to apply the high voltage to the memorygate electrode 13 of the writing selected memory cell and avoid theapplication of the high voltage to the memory gate electrode 13 of thenon-selected memory cell adjacent to the writing selected memory cell inthe Y direction with the source region 20 interposed therebetween.

Thus, the present embodiment is different from the first comparativeexample in that since no high voltage is applied to the memory gateelectrode 13 of the non-selected memory cell adjacent to the selectedmemory cell to be written in the Y direction with the source region 20interposed therebetween, it is possible to prevent electrons from beingcaptured into the insulating film 11 (silicon nitride film 11 b thereof)of the non-selected memory cell, and prevent the phenomenon that thethreshold voltage of the memory transistor of the non-selected memorycell. Thus, the present embodiment is capable of preventing writedisturb applied to the non-selected memory cell adjacent to the writeselected memory cell in the Y direction with the source region 20interposed therebetween.

FIG. 11 is a graph showing write disturb of a non-selected memory cellat the operation of writing into a selected memory cell. The horizontalaxis of FIG. 11 corresponds to time (arbitrary unit) subsequent to theapplication of a writing voltage, whereas the vertical axis of FIG. 11corresponds to a threshold voltage (arbitrary unit) of the non-selectedmemory cell adjacent to the selected memory cell intended for writing inthe Y direction with the source region 20 interposed therebetween. Acase (indicated by a solid line as “present embodiment” in the graph ofFIG. 11) corresponding to the semiconductor device according to thepresent embodiment such as shown in FIGS. 1 through 3 and a case(indicated by a dotted line as “first comparative example” in the graphof FIG. 11) corresponding to the first comparative example such as shownin FIGS. 8 and 9 are shown in the graph of FIG. 11.

In the first comparative example as shown in the graph of FIG. 11, upona write operation, a high voltage is applied to each of the sourceregion 20 and the memory gate electrode 13 in the non-selected memorycell adjacent to the writing selected memory cell in the Y directionwith the source region 20 interposed therebetween. Therefore, electrons(hot electrons) are captured into the insulating film 11 (siliconnitride film 11 b thereof) of the non-selected memory cell and hence thethreshold voltage of the memory transistor for the non-selected memorycell rises. In the present embodiment in contrast, no high voltage isapplied to the memory gate electrode 13 upon a write operation in thenon-selected memory cell adjacent to the writing selected memory cell inthe Y direction with the source region 20 interposed therebetween.Therefore, no electrons (hot electrons) are captured into the insulatingfilm 11 (silicon nitride film 11 b thereof) of the non-selected memorycell and hence the threshold voltage of the memory transistor for thenon-selected memory cell almost remains unchanged.

Thus, in the present embodiment, the memory gate lines 14 (memory gateelectrodes 13) adjacent to each other in the Y direction with the sourceregion 20 interposed therebetween are not electrically connected to eachother. The desired potentials (different potentials) can independentlybe supplied to the two memory gate lines 14 (memory gate electrodes 13),respectively, adjacent to each other with the source region 20interposed therebetween. It is therefore possible to prevent theapplication of the high voltage to the memory gate electrode 13 in thenon-selected memory cell adjacent to the writing selected memory cellwith the source region 20 interposed therebetween and prevent a change(rise) in the threshold voltage of the memory transistor for thenon-selected memory cell. Thus, the performance of the semiconductordevice can be enhanced.

FIG. 12 is a fragmentary plan view of a semiconductor device(nonvolatile semiconductor memory device) showing a second comparativeexample discussed by the present inventors, and FIG. 13 is a fragmentarysectional view thereof, respectively. A sectional diagram taken alongline D-D of FIG. 12 corresponds to FIG. 13. FIG. 12 is a plan viewcorresponding to FIGS. 1 and 8.

The semiconductor device of the second comparative example shown inFIGS. 12 and 13 is different from the semiconductor device according tothe present embodiment in terms of pattern shapes of select gate lines 9and memory gate lines 14 and positions of contact holes 23 f connectedto the memory gate lines 14 and plugs 24 f that bury them. Since asectional structure of each memory cell of the semiconductor deviceaccording to the second comparative example is similar to that of FIG. 2of the first embodiment, its explanation will be omitted herein.

In the semiconductor device of the second comparative example shown inFIGS. 12 and 13, pattern shapes of polycrystalline silicon films 6 thatconstitute select gate electrodes 8 and the select gate lines 9 aresubstantially similar to the first comparative example. That is, thepattern shapes of the select gate lines 9 are substantially similar tothe first comparative example. The select gate lines 9 respectively havefirst portions 9 a that connect the select gate electrodes 8 of memorycells 30 extending in an X direction (corresponding to the X directionof FIG. 1) of FIG. 12 and arranged in the X direction, and wide portions9 c each relatively broad in width at the first portion 9 a. However,the select gate lines 9 are not provided with the second portions 9 bunlike the present embodiment. In the semiconductor device of the secondcomparative example, each of the memory gate lines 14 each constitutedof a polycrystalline silicon film 12 is formed on one sidewall of eachof the select gate lines 9 with an insulating film 11 interposedtherebetween. However, the memory gate lines 14 do not include suchcontact sections 14 b as shown in the first comparative example unlikethe first comparative example. Hence the memory gate lines 14 adjacentto each other in the Y direction with a source region 20 interposedtherebetween are not electrically connected to each other.

In the semiconductor device of the second comparative example shown inFIGS. 12 and 13, each of the memory gate lines 14 has a contact section14 c that extends in a Y direction (corresponding to the Y direction ofFIG. 1) of FIG. 12 from over the select gate line 9 adjacent to thememory gate line 14 with the corresponding insulating film 11 interposedtherebetween to over an element isolation region 2. The contact section14 c of the memory gate line 14 is not connected to other memory gatelines 14 adjacent to the memory gate line 14 in the Y direction with thesource region 20 interposed therebetween. Thus, the memory gate lines 14are respectively provided with the independent contact sections 14 c.

The polycrystalline silicon films 12 formed over a semiconductorsubstrate 1 so as to cover the patterned polycrystalline silicon films 6that constitute the select gate electrodes 8 and the select gate lines 9are anisotropically etched to allow the polycrystalline silicon films 12to remain on one sidewalls of the patterned polycrystalline siliconfilms 6 with the insulating films 11 interposed therebetween.Consequently, the corresponding memory gate electrodes 13 and memorygate lines 14 each formed of the polycrystalline silicon film 12 can beformed. On the other hand, however, an etching mask layer (photoresistlayer not shown) is formed over the contact sections 14 c and thepolycrystalline silicon films 12 placed below the etching mask layer arecaused to remain in the process of anisotropically etching thepolycrystalline silicon films 12, whereby the contact sections 14 c forthe select gate lines 9 are formed. Thus, the plan pattern shape of theetching mask layer (photoresist layer) used at this time corresponds tothat of each contact section 14 c.

The contact holes 23 f are formed over their corresponding contactsections 14 c of the memory gate lines 14 employed in the semiconductordevice of the second comparative example. The plugs 24 f are connectedto their corresponding contact sections 14 c of the memory gate lines 14at the bottoms of the contact holes 23 f. The plugs 24 f are connectedto their corresponding wirings 25.

In the semiconductor device of the second comparative example shown inFIGS. 12 and 13 in a manner similar to the present embodiment, thememory gate lines 14 adjacent to each other in the Y direction with thesource region 20 interposed therebetween are not electrically connectedto each other. Desired voltages (different voltages) can independentlybe applied to the memory gate lines via the different wirings 25 andplugs 24 f. Therefore, upon a write operation, even the semiconductordevice of the second comparative example is capable of preventing theapplication of a high voltage to the memory gate electrode 13 in anon-selected memory cell adjacent to a writing selected memory cell inthe Y direction with the corresponding source region 20 interposedtherebetween and prevent a change (rise) in the threshold voltage of amemory transistor for the non-selected memory cell, in a manner similarto the present embodiment.

However, the semiconductor device of the second comparative exampleshown in FIGS. 12 and 13 are different from the semiconductor deviceaccording to the present embodiment in that the select gate lines 9 arenot provided with the second portions 9 b respectively and the contactsections 14 c of the memory gate lines 14 extend in the Y direction ofFIG. 12. Therefore, a margin for alignment and a margin for a variationin size in a photolithography process concentrate on the Y direction ofFIG. 12 alone in the case of a plane layout of the semiconductor deviceof the second comparative example shown in FIGS. 12 and 13. Thus, thereis a possibility that it will be hard to sufficiently ensure a processmargin and the production yields of the semiconductor device will bedegraded. Attempting to sufficiently ensure the process margin in orderto prevent the degradation of the manufacturing yields of thesemiconductor device will incur upsizing of the semiconductor device (agreat increase in the area of the plane layout). In the semiconductordevice of the second comparative example, for example, margins for aphotolithography process for patterning the polycrystalline silicon film6 to form the select gate electrodes 8 and the select gate lines 9, aphotolithography process for forming the contact sections 14 c uponanisotropically etching the polycrystalline silicon film 12 to form thememory gate electrodes 13 and the memory gate lines 14, aphotolithography process for forming the contact holes 23 f, etc. arestacked on one another only in the Y direction of FIG. 12.

In the semiconductor device according to the present embodiment shown inFIGS. 1 through 3 in contrast, the select gate lines 9 respectively havethe second portions 9 b that extend in the Y direction of FIG. 1, andthe contact sections 14 a of the memory gate lines 14 respectivelyextend in the X direction of FIG. 1 from over the second portions 9 b ofthe select gate lines 9 to over the element isolation region 2.

That is, in the present embodiment, the select gate lines 9 respectivelyhave not only the first portions 9 a that connect the select gateelectrodes 8 of the respective memory cells 30 extending in the Xdirection of FIG. 1 and arranged in the X direction to one another andthe wide portions 9 c at which the widths of the first portions 9 a arerelatively broad and on which the contact holes 23 c are formed, butalso the second portions 9 b which are respectively connected to thefirst portions 9 a extending in the X direction of FIG. 1 and extend inthe Y direction (the direction orthogonal to the X direction) of FIG. 1.Accordingly, the second portions 9 b of the select gate lines 9 have oneends connected to the first portions 9 a and extend in the direction (Ydirection) substantially orthogonal to the extending direction (Xdirection) of the first portions 9 a. While the memory gate lines 14each formed of the polycrystalline silicon film 12 are formed over theircorresponding sidewalls of both the first portions 9 a of the selectgate lines 9 and the wide portions 9 c of the second portions 9 b, thememory gate lines 14 respectively have the contact sections 14 a thatextend in the X direction of FIG. 1 from over the second portions 9 b ofthe select gate lines 9 to over the element isolation region 2.

In the present embodiment, the select gate lines 9 respectively have thesecond portions 9 b that extend in the Y direction of FIG. 1. Thecontact sections 14 a of the memory gate lines 14 are respectivelyformed so as to extend in the X direction of FIG. 1 from over the secondportions 9 b of the select gate lines 9 to over the element isolationregion 2. Therefore, a margin for alignment and a margin for a sizevariation in a photolithography process are dispersed into the X and Ydirections of FIG. 1 and a process margin is easily ensuredsufficiently. Therefore, the production yields of the semiconductordevice can be enhanced. It is also possible to improve the reliabilityand performance of the semiconductor device. When the margin foralignment and the margin for the size variation in the photolithographyprocess concentrate on the Y direction of FIG. 1 alone as in the secondcomparative example, there is a need to make relatively large theinterval between the memory gate lines 13 adjacent to each other in theY direction. Since, however, the margin for alignment and the margin forthe size variation in the photolithography process can be dispersed intothe X and Y directions of FIG. 1 in the present embodiment, the intervalbetween the memory gate lines 13 adjacent to each other in the Ydirection can be made relatively small, thus leading to the advantage ofreducing the area of a plane layout. Thus, the semiconductor device canbe made small-sized. It is also possible to improve the productionyields of the semiconductor device. In the nonvolatile semiconductormemory device, there is an allowance for space as viewed in the Xdirection corresponding to the direction of each word line, and there isno allowance for space as viewed in the Y direction corresponding to thedirection of each bit line. Therefore, the contact sections 14 a of thememory gate lines 14 are caused to extend in the X direction in whichthere is relatively an allowance for space as in the present embodiment,rather than allowing the contact sections 14 c of the memory gate lines14 to extend in the Y direction in which there is no allowance for spaceas in the second comparative example. Consequently, the productionyields of the semiconductor device can be enhanced and a reduction inthe entire layout area of the nonvolatile semiconductor memory device isalso enabled.

A process for manufacturing the semiconductor device (nonvolatilesemiconductor memory device) according to the present embodiment willnext be explained with reference to the accompanying drawings. FIGS. 14through 25 are respectively fragmentary sectional views being in themanufacturing process of the semiconductor device (nonvolatilesemiconductor memory device) according to the present embodiment. OfFIGS. 14 through 25, FIGS. 14, 16, 18, 20, 22 and 24 are respectivelysectional views of regions each corresponding to FIG. 2, and FIGS. 15,17, 19, 21, 23 and 25 are respectively sectional views of regions eachcorresponding to FIG. 3. FIGS. 14 and 15 are respectively sectionalviews being in the same manufacturing process, FIGS. 16 and 17 arerespectively sectional views being in the same manufacturing process,FIGS. 18 and 19 are respectively sectional views being in the samemanufacturing process, FIGS. 20 and 21 are respectively sectional viewsbeing in the same manufacturing process, FIGS. 22 and 23 arerespectively sectional views being in the same manufacturing process,and FIGS. 24 and 25 are respectively sectional views being in the samemanufacturing process.

As shown in FIGS. 14 and 15, a semiconductor substrate (semiconductorwafer) 1 comprising p-type monocrystalline silicon or the like havingspecific resistivity ranging from approximately 1 to 10 Ωcm, forexample, is first prepared. Then, an element isolation region 2comprising an insulator is formed over a main surface of thesemiconductor device 1 by, for example, an STI (Shallow TrenchIsolation) method or the like.

Next, a p-type impurity is ion-implanted to form a p-type well 3. Thep-type well 3 is principally formed in a memory cell region or area 1A.The memory cell region 1A is electrically isolated from other region bythe element isolation region 2. Then, a p-type semiconductor region(p-type impurity region and channel region) 4 for adjusting thethreshold voltage of a selection transistor is formed in a surfaceportion (surface layer portion) of the p-type well 3 by an ionimplantation method or the like.

Next, the surface of the semiconductor substrate 1 is subjected tocleaning processing and thereafter an insulating film 5 a for a gateinsulating film of each selection transistor is formed over the surfaceof the p-type well 3 by a thermal oxidation method or the like. Then, apolycrystalline silicon film 6 formed as select gate electrodes and asilicon oxide film 7 for protection of the select gate electrodes aresequentially deposited over the semiconductor substrate 1 containing aportion above the insulating film 5 a. The polycrystalline silicon film6 is of a polycrystalline silicon film implanted or doped with an n-typeimpurity (e.g., phosphorus (P) or the like), i.e., an n-typepolycrystalline silicon film.

Next, the silicon oxide film 7 and the polycrystalline silicon film 6are patterned by using photolithography technology and dry etchingtechnology to form select gate electrodes 8 and select gate lines 9 ofselection transistors. The select gate electrodes 8 and select gatelines 9 are constituted of the patterned polycrystalline silicon films6. The insulating film 5 a placed below the select gate electrodes 8result in the gate insulating films 5 for the selection transistors.Thus, the select gate electrodes 8 and select gate lines 14 (first,second and third portions 14 a, 14 b and 14 c) are formed in the sameprocess and comprise conductor layers (polycrystalline silicon films 6)identical in layer. Upon formation of patterns for the select gateelectrodes 8 and the select gate lines 9, dry etching is stopped in thestage of exposure of the surface of the insulating film 5 a in such amanner that unnecessary damage does not occur in the surface of thesemiconductor substrate 1.

Next, as shown in FIGS. 16 and 17, a threshold voltage adjusting p-typesemiconductor region (p-type impurity region) 10 is formed in a channelregion of each memory transistor of the semiconductor substrate 1(p-type well 3 thereof) by the ion implantation method or the like.

Next, the insulating film 5 a left behind for protection of thesemiconductor substrate 1 is removed using, for example, hydrofluoricacid or the like, and thereafter an insulating film 11 used as the gateinsulating film for each memory transistor is formed. The insulatingfilm 11 is constituted of a laminated film of, for example, a siliconoxide film (corresponding to the silicon oxide film 11 a), a siliconnitride film (corresponding to the silicon nitride film 11 b) and asilicon oxide film (corresponding to the silicon oxide film 11 c). Theinsulating film 11 is formed over the surface of the p-type well 3 andthe exposed surfaces (sidewalls) of the select gate electrodes 8. Of theinsulating film 11, the silicon oxide film can be formed by, forexample, an oxidation process (thermal oxidation process), and thesilicon nitride film can be formed by, for example, a CVD (ChemicalVapor Deposition) method. It is possible to deposit the silicon nitridefilm of the insulating film 11 by the CVD method after the formation ofthe lower silicon oxide film of the insulating film 11 by thermaloxidation and form the upper silicon oxide film of the insulating film11 by the CVD method and thermal oxidation. Incidentally, the siliconoxide film 7 provided over each select gate electrode 8 can also beremoved upon removal of the insulating film 5 a.

Next, a polycrystalline silicon film 12 used as each memory gateelectrode is deposited over the semiconductor substrate 1 containing theinsulating film 11. The polycrystalline silicon film 12 is of apolycrystalline silicon film implanted or doped with an n-type impurity(e.g., Phosphorous (P) or the like), i.e., an n-type polycrystallinesilicon film.

Next, the polycrystalline silicon film 12 is removed by anisotropicetching technology until the upper surface of the insulating film isexposed, thereby causing the polycrystalline silicon film 1 to remainover the sidewalls of the select gate electrodes 8 and the select gatelines 9 through the insulating film 11, so that the corresponding memorygate electrodes 13 and memory gate lines 14 are formed. The insulatingfilm placed below each memory gate electrode 13 results in a gateinsulating film for each memory transistor. In the process ofanisotropically etching the polycrystalline silicon film 12, an etchingmask layer (photoresist layer no shown) is formed over the contactsections 14 a, and the polycrystalline silicon film 12 placed below theetching mask layer is caused to remain, whereby the contact sections 14a of the select gate lines 9 are formed. Thus, the memory gateelectrodes 13, the memory gate lines 9 and the contact sections 14 a ofthe memory gate lines 14 are formed in the same process and compriseconductor layers (polycrystalline silicon film 12) identical in layer.Sidewall spacers 15 each comprising the polycrystalline silicon film 12are formed even over their corresponding sidewalls of the select gateelectrodes 8 on the sides opposite to the memory gate electrodes 13.

Next, as shown in FIGS. 18 and 19, the sidewall spacers 15 are removedby using the photolithography technology and dry etching technology.Then, the upper silicon oxide film of the exposed insulating film 11 andthe lower silicon nitride film thereof are removed using, for example,hydrofluoric acid and thermal phosphoric acid or the like.

Next, as shown in FIGS. 20 and 21, a low-concentration n-type impurityis ion-implanted to form low-concentration n-type semiconductor regions16 at drain sections and form low-concentration n-type semiconductorregions 17 at source sections. Although the low-concentration n-typesemiconductor regions 16 at the drain sections and the low-concentrationn-type semiconductor regions 17 at the source sections are formed in thesame ion-implantation process, they can also be formed by discreteion-implantation processes using the photolithography technology and aresist film.

Next, the exposed portion of the lower silicon oxide film of theinsulating film 11 is removed by, for example, hydrofluoric acid or thelike. Thereafter, the silicon oxide film is deposited over thesemiconductor substrate 1 and anisotropically etched to form sidewallspacers 18 each formed of an insulator such as silicon oxide over theircorresponding sidewalls of the select gate electrode 8, the select gateline 9, the memory gate electrode 13 and the memory gate line 14.

Next, an n-type impurity is ion-implanted to form drain regions (n-typesemiconductor region and n-type impurity region) 19 of the selectiontransistors and source regions (n-type semiconductor region and n-typeimpurity region) 20 of the memory transistors. Each of the drain regions19 is higher than the low-concentration n-type semiconductor region 16at the drain section in impurity concentration, and each of the sourceregions 20 is higher than the low-concentration n-type semiconductorregion 17 at the source section. Thus, memory cells 30 for a flashmemory (nonvolatile semiconductor memory device) are formed.

Next, as shown in FIGS. 22 and 23, the surfaces of the select gateelectrodes 8, select gate lines 9, memory gate electrodes 13, memorygate lines 14, drain regions 19 and source regions 20 are exposed, and,for example, a cobalt (Co) film is deposited and heat-treated to therebyform a metal silicide film (cobalt silicide film, e.g., CoSi₂ film) 21over their corresponding upper portions (surfaces) of the select gateelectrodes 8, select gate lines 9, memory gate electrodes 13, memorygate lines 14, drain regions 19 and source regions 20 respectively.Thus, diffusion resistances and contact resistances can be brought intolow resistance form. Thereafter, the unreacted cobalt film is removed.

Next, as shown in FIGS. 24 and 25, an insulating film (interlayerinsulating film) 22 is formed over the semiconductor substrate 1. Thatis, the insulating film 22 is formed over the semiconductor substrate 1containing over the metal silicide film 21 so as to cover the selectgate electrodes 8 and the memory gate electrodes 13. The insulating film22 is constituted of a laminated film of, for example, relatively thinsilicon nitride 22 a and relatively thick silicon oxide 22 b providedthereon. The insulating film 22 can serve as the interlayer insulatingfilm. As needed, the process of planarizing the upper surface of theinsulating film 22 can also be carried out by a CMP (Chemical MechanicalPolishing) method or the like.

Next, the insulating film 22 is dry-etched using the photolithographytechnology and the dry etching technology to define contact holes 23 inthe insulating film 22.

Next, plugs 24 (containing the interiors of plug 24) each made up oftungsten (W) or the like are formed in the contact holes 23. The plugs24 can be formed by, for example, forming a barrier film (e.g., titaniumnitride film) over the insulating film 22 containing the interiors ofthe contact holes 23, thereafter forming a tungsten film over thebarrier film by the CVD method so as to bury the contact holes 23, andremoving the unnecessary tungsten film and barrier film placed over theinsulating film 22 by CMP or an etchback method or the like.

Next, a wiring (first wiring layer) 25 is formed over the insulatingfilm 22 in which the plugs 24 have been embedded. For example, a barrierconductor film 25 a (e.g., titanium film or titanium nitride film orlaminated film thereof), an aluminum film 25 b and a barrier conductorfilm 25 c (e.g., titanium film or titanium nitride film or laminatedfilm thereof) are sequentially formed over the insulating film 22 withthe plugs 24 embedded therein by a sputtering method or the like andpatterned by using the photolithography technology and dry etchingtechnology or the like to enable formation of each wiring 25. The wiring25 is not limited to such an aluminum wiring as described above and canbe changed in various ways. The wiring 25 may also be formed as, forexample, a tungsten wiring and a copper wiring (e.g., buried copperwiring formed by the damascene method). Although an interlayerinsulating film, an upper wiring layer, etc are further formedsubsequently, their explanations will be omitted here. Ones subsequentto a second layer wiring may also be configured as a buried copperwiring formed by the damascene method.

Second Preferred Embodiment

FIG. 26 is a fragmentary plan view of a semiconductor device(nonvolatile semiconductor memory device) according to a secondembodiment of the present invention. FIG. 26 is a plan viewsubstantially corresponding to FIG. 1 of the first embodiment. Since asectional structure or the like of each memory cell is similar to thefirst embodiment, its description will be omitted herein.

While the memory gate lines 14 (polycrystalline silicon films 12) havebeen electrically connected via the wiring 25 and the plugs 23 d onalternate lines, memory gate lines 14 (polycrystalline silicon films 12)are electrically connected to one another via the wirings 25 and plugs23 d at intervals of seven lines in the semiconductor device of thepresent embodiment shown in FIG. 26. That is, other seven memory gatelines 14 exist between the memory gate lines 14 electrically connectedto one another.

In the semiconductor device shown in FIG. 26, the positions of secondportions 9 b of select gate lines 9, and the positions of contactsections 14 a of the memory gate lines 14 placed over the sidewalls ofthe select gate lines 9 are shifted respectively to thereby shiftX-direction positions of contact holes 23 d opened over the contactsections 14 a of the respective memory gate lines 14. Thus, theconnected positions of the contact sections 14 a of the memory gatelines 14 adjacent to each other in a Y direction and their correspondingplugs 24 d are shifted in an X direction. The positions in the Xdirection, of connecting portions of the contact sections 14 a of thememory gate lines 14 and their corresponding plugs 24 d are madeidentical at nth, and n+8th to n+8mth (where n and m: integers) memorygate lines 14. The nth and n+8th to n+8mth memory gate lines 14 areelectrically connected to one another by the same wirings 25 extendingin the Y direction. By shifting the positions of the second portions 9 bof the respective select gate lines 9, and the positions of the contactsections 14 a of the memory gate lines 14 placed over the sidewalls ofthe select gate lines 9 respectively and shifting the X-directionpositions of the contact holes 23 d opened over the contact sections 14a of the respective memory gate lines 14, the respective memory gatelines 14 can be electrically connected to desired wirings 25 extendingin the Y direction.

Incidentally, although the memory gate lines 14 are connected to thewirings 25 on alternate lines in the first embodiment, and the memorygate lines 14 are connected to the wirings 25 at intervals of sevenlines in the present embodiment, the memory gate lines 14 can beconnected to the wirings 25 at intervals of the number of linesaccording to need.

The present embodiment can also obtain an advantageous effectsubstantially similar to the first embodiment.

While the invention made above by the present inventors has beendescribed specifically on the basis of the preferred embodiments, thepresent invention is not limited to the embodiments referred to above.It is needless to say that various changes can be made thereto withoutthe scope not departing from the gist thereof. Although the split gatetype memory cell using the MONOS has been explained in the presentembodiment, for example, it can also be applied to a 1 transistor typeNOR type flash memory or the like.

This invention is suitable for application to a semiconductor deviceincluding a nonvolatile semiconductor memory device.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate having a main surface; and a first nonvolatilememory cell and a second nonvolatile memory cell formed on the mainsurface of the semiconductor substrate, each of the first and secondnonvolatile memory cells including a first MIS transistor for storingdata and a second MIS transistor for selecting the first MIS transistor;wherein a first gate electrode of the first MIS transistor of the firstnonvolatile memory cell and a first gate electrode of the first MIStransistor of the second nonvolatile memory cell extend in a firstdirection so as to sandwich a common source region of the first MIStransistors of the first and second nonvolatile memory cells in a planview, wherein the first gate electrode of the first MIS transistor ofthe first nonvolatile memory cell has a first contact portion extendingin a second direction substantially perpendicular to the first directionin the plan view to provide an electrical contact thereto, and the firstcontact portion extends to be adjacent to the first gate electrode ofthe first MIS transistor of the second nonvolatile memory cell, whereinthe first gate electrode of the first MIS transistor of the secondnonvolatile memory cell has a second contact portion extending in thesecond direction in the plan view to provide an electrical contactthereto, and the second contact portion extends to be adjacent to thefirst gate electrode of the first MIS transistor of the firstnonvolatile memory cell, and wherein the first contact portion and thesecond contact portion are arranged in an offset relation to each otherin the first direction and in an overlap relation in the seconddirection, so that a portion of an edge of the first contact portionfaces, and is spaced apart from in the first direction, a portion of anedge of the second contact portion in an opposing relationship.
 2. Asemiconductor device according to the claim 1, wherein a first gateinsulating film of the first MIS transistor of the first nonvolatilememory cell is formed between the semiconductor substrate and the firstgate electrode of the first MIS transistor of the first nonvolatilememory cell, the first gate insulating film of the first MIS transistorof the first nonvolatile memory cell having a charge storage portion,and wherein a first gate insulating film of the first MIS transistor ofthe second nonvolatile memory cell is formed between the semiconductorsubstrate and the first gate electrode of the first MIS transistor ofthe second nonvolatile memory cell, the first gate insulating film ofthe first MIS transistor of the second nonvolatile memory cell having acharge storage portion.
 3. A semiconductor device according to the claim2, wherein the charge storage portion of the first gate insulating filmof the first MIS transistor of the first nonvolatile memory cell and thecharge storage portion of the first gate insulating film of the firstMIS transistor of the second nonvolatile memory cell each include asilicon nitride film.
 4. A semiconductor device according to the claim1, wherein each of the second MIS transistors of the first and secondnonvolatile memory cells includes a second gate insulating film and thesecond gate electrode, the second gate insulating film being formedbetween the semiconductor substrate and each of the second gateelectrodes, wherein each of the first MIS transistors of the first andsecond nonvolatile memory cells includes a first gate insulating film,the first gate insulating film being formed between the semiconductorsubstrate and each of the first gate electrodes and between each of thesecond gate electrodes and each of the first gate electrodes, and beinga charge storage portion, and wherein each of the first gate electrodesis formed in a sidewall form.
 5. A semiconductor device according to theclaim 4, wherein a length of each of the first gate electrodes issmaller than a length of each of the second gate electrodes in thesecond direction.
 6. A semiconductor device according to the claim 1,wherein each of the second MIS transistors of the first and secondnonvolatile memory cells includes a second gate electrode, and wherein alength of each of the first gate electrodes is smaller than a length ofeach of the second gate electrodes in the second direction.
 7. Asemiconductor device according to the claim 1, wherein the elementisolation region is formed of an insulating film embedded into a trenchformed on the main surface of semiconductor substrate, and wherein thefirst and second contact portions are formed over the element isolationregion.
 8. A semiconductor device according to claim 1, wherein thefirst gate electrode of the first MIS transistor of the firstnonvolatile memory cell is independent from, and electricallyunconnected to, the first gate electrode of the first MIS transistor ofthe second nonvolatile memory cell so that the first and second contactportions are independent from and electrically unconnected to eachother.